Quake prediction remains tricky

Videos
Photos

(Xinhua)
Updated: 2008-05-21 08:08

WASHINGTON - After last week's deadly earthquake in Sichuan province, quake prediction has become an issue of growing public concern.

However, making accurate short-term predictions remains "very difficult", said Lucile Jones, a seismologist with the US Geological Survey (USGS).

When asked what factors affect earthquake prediction, she said: "This depends on what you mean by predict."

On the spatial distribution - that is, indicating likely locations for earthquakes - "we (seismologists) do an excellent job", Jones said.

However, when it comes to time and magnitude, prediction becomes more difficult.

Magnitude is determined only during an earthquake by measuring how far the rupture that starts at the epicenter moves down the fault, she said.

If the rupture travels 100 meters, it will be about magnitude 4. If it travels 300 km, the quake will be close to magnitude 8, said Jones.

But what stops the earthquake may not be linked to what starts it, so information about a quake's magnitude can't be determined before it begins.

"Short-term (prediction) is difficult unless the earthquake has a foreshock," she said.

Smaller earthquakes occurring near the initial one are called aftershocks.

Triggered earthquakes are only 5 percent of the time bigger than the first ones. The first one is then called a foreshock, and the triggered event is the mainshock.

Jones said the probability of a subsequent quake increases after the first one, meaning the success rate of prediction for the triggered event would be relatively higher.

The USGS' website shows the real-time probability of aftershocks in the state of California after a triggering event, said Jones, who is USGS' chief scientist of the Multi Hazards Demonstration Project for Southern California.

Long-term prediction of earthquakes is fairly mature relative to short-term prediction and is usually based on fault history. Governments can develop building codes according to the long-term prediction results in specific areas.

Sometimes, there are precursors to quakes, such as unusual animal behavior or strange astronomical phenomena, Jones said, adding there is no scientific evidence to support this.

"Every effort to prove these has shown there is no solid signal," Jones said.

She said believed the most important step governments could take to improve the state of earthquake prediction would be to invest more in earthquake research.